Why so many? Preventable diseases, like measles, are partly to blame. There’s a vax for that, but for impoverished kids who don’t get it contracting the disease can impair their hearing. And that’s just one example – there are diseases like maternal rubella that can harm pregnant women, impacting their unborn children. And of course, accidents in adulthood and aging.

Of all those millions who can’t hear well, only 10 percent have access to hearing aids.

Why so few? Plenty of reasons – from expensive hearing aids to a lack of trained audiologists. There’s the perception that hearing loss (like wrinkles and gray hairs) just comes with aging, so just suck it up , says Gabrielle H. Saunders, the associate director and investigator at the National Center for Rehabilitative Auditory Research at the Portland VA Medical Center in Oregon. Veterans have hearing aids covered, and still 40 percent of those who could benefit don’t get them, she says.

So what’s the solution? It might just be the smart phone.

No one’s declaring victory over sub-Saharan hearing loss yet, but a host of hearing projects , many of them aimed at the developing world, are taking advantage of mobile tech. Some companies want to create in-ear devices that, when paired with a smart phone, act like a rechargeable hearing aid. Another app would help fit hearing aids, acting as a pseudo audiologist to asses a patient’s hearing levels and other issues in order to fit the right device.

One Australian company is even working to develop a self-contained kit that would allow a person to test their own hearing – no expert, or smart phone, needed.

But it’s not just the global south that’s likely to benefit. There’s a boomerang effect. Americans may have better access to audiologists, doctors and hearing aid supplies, but insurance often doesn’t cover much (and many people just don’t bother). Which means new solutions built remote Indian villages could work double-wonders, reworking how urbane Americans hear, too.